Last summer, our refrigerator stopped working. Alarmed that the entire contents of the fridge may be lost, we moved everything from the freezer to another freezer that was in the pantry. But the contents of the refrigerator were more of a problem. A couple of picnic coolers would suffice for a couple of hours, but not for days.
My son (a student in a university EE program) and I disassembled the rear of the freezer section, and we found the condenser coils frozen, so they were working correctly. The actual cause of the failure was that the circulating fan had stopped. Without the circulating fan, the cold air from the coils does not chill either the freezer or the refrigerator section below. The appliance was crippled.
Thinking the motor bearings might be seized, we took out the motor to lubricate it, and we found that the fan turned easily. It was not the bearings. When we checked the continuity of the motor windings, we discovered that it was an open circuit.
At least now we knew we had to replace the motor. It would take two or three days for the new motor to arrive, and, in the meantime, we would have no refrigerator. This is a big deal when you have four boys living at home.
While I went online to find a replacement for the motor, my son, not knowing any better, decided to unwrap the insulation tape on the motor and see what he could do. The motor has hundreds of turns of fine enameled wire, about 32 gauge, on a plastic core. I figured an open circuit was probably buried under dozens of layers. However, upon removing the tape, my son found an obviously melted wire on the surface of the windings.
I thought this would be a great time to explain to him what happens when a transformer gets one shorted turn. Magnetically, this one turn shorted out the whole transformer, which is why there was enough energy to melt the copper wire into metal balls. The enameled insulation was so thin that the motor vibration must have been enough to chafe the insulation of two adjacent or overlapping wires, causing a shorted turn, which then melted to form an open circuit.
My son did not assume my belief that the motor was ruined, and proceeded to unwrap about two turns in each direction. He asked me to solder it back together. Finally, a light bulb went off. I realized that you can repair small motors if you can access the bad windings, so we soldered the wires back together, and voila! The motor worked again. It had three fewer windings, but out of, say, 300 windings, this is a miniscule change.
We were able to reassemble the refrigerator/freezer and get the food chilling. The lesson? Don’t assume it’s impossible just because you've never done it before. The spare motor arrived three days later. It’s in the shop now, waiting for the next (unfixable) failure.
This entry was submitted by Chris Kelly and edited by Rob Spiegel.
Chris Kelly holds a BS from the University of New Mexico and an MS in computer science from Colorado State University. He has served as a design engineer with Agilent Technology since 1983, and he designs small electronic instruments, such as function generators, and DMMs. He has been named on six US patents in the areas of data acquisition and conversion, instrument calibration, and signal generation.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
We seemed to slide into the no-fix-it mentality when kids stopped taking home-ec and shop in school and when parents became so protective they wouldn't let their kids "do stuff" that involved tools, chemicals, or electricity. I grew up in the Sputkin era when kids tinkered with cars, built electrical and electronic "stuff," and experimented with chemistry sets in basement labs. Thomas Edison was my hero.
My brothers and I used hand tools and watched our dad, uncle, and grandfather make and fix things. A friend's dad had a small metal lathe, drill press, and other tools that we felt comfortable around and learned to use. Mom used to complain that my brother Chris and I brought home more junk from the local dump than we took. We disassembled washing machines and lawnmowers for motors and stripped TVs and radios for parts--that is, if we couldn't repair them.
Unless we instill a hands-on do-it-yourself attitude in young people fewer and fewer adults will have the interest or aptitude to fix things, let alone design them.
Like an old Navy Chief used to say - "what's it gonna do, not work?"
Maybe I'm showing my geek, but someone tossing out a 'broke' appliance was giving me a gift! Bigger problem was where to put it at home...
Guess things are different these days, but you don't learn medicine by keeping your hands clean. Grab the broke gear and tear into it, find out what and where.
I'm with you on this one, Jon. If I didn't have the willingness to fix things, my first car -- a Corvair -- would not have lasted two weeks. I literally had a rubber band holding the choke in place. I grew up believing that you first try it fix it yourself before taking it in for repair. It was pretty much culture-wide when I was a kid.
By the way, gift subscriptions to Popular Science or Popular Mechanics (perhaps both!) might spark a kid's interest in DYI projects and learning how to use tools. I just learned an interesting trick to silence noisy chains in the March issue of PM.
I am impressed that the repair was that simple. What I have been finding for a few years now is that the design skimps on copper and skimps on iron, and so when the line voltage rises a bit the iron saturates and the current rises and there is a failure exactly as described. Of course, sometimes poor insulation makes things fail even faster. But the most common response of the manufacturer has been to put in a nonresettable thermal fuse, usually implanted in the winding where it is hard to find. REmoving the failed thermal fuse and adding a regular fuse will often repair the system, and assure that it is still safe and won't start a fire if it fails. Of course on many occasions the thermal fuse just gets bypassed. Yes, the product may fail again some time, but I have not had it happen yet.
I am wondering where these thermal fuses come from, they usually have no markings, and I really wonder where I can buy some of them. My guess is that they are poorly calibrated and that is what causes the failures.
Like others, I too, have had similar experiences fixing "stuff." I hope all our experiences are symptomatic of a spirit of willingness to try to fix things instead of running out to buy a new model which many times is no better or even worse than what we are trying to fix. In that spirit, opportunities abound, and here in the Chicago area, an entrepreneur has expanded his 16 year old company (corecentricsolutions.com, Think Green division) to include the remanufacture of "no longer serviced" parts for appliances such as stoves, refrigerators, etc. This gives the DIYer a chance to keep equipment running. As the Brits would say, "Full marks" to all of those willing to try to fix a broken, but otherwise good piece of gear.
Good idea for a gift, Jon. There are also a number of new science shows on TV these days. Even "Mythbusters" gets into a bit of science and engineering.
Hi, Rob. Although toy stores don't sell chemistry sets today, parents can buy many fun kits and activity "packages" for kids interested in science and technology. Science Kit lists many, as does Ramsey Electronics and Jameco Electronics. Perhaps some CAD-and-animation experts can create graphic "construction" projects that let kids assemble a small motor in virtual space. The software would include the pieces and have the kids assemble them in the right order to create something that works. Simple projects such as a wind-powered generator, weed-wacker 2-cycle engine, small generator, and so on would get kits interested enough they could start to do things with real tools. Lightwave 3D, for example, can create and animate solid objects nicely.
Good suggestions, Jon. It was a tad easier when I was a kid and there were tons of science-based toys. There were also tons of build-it-yourself kits such as Heathkit. Heathkit is still around, but it's not as easily available as before.
This is a bit of a tangent, biy I had a vaguely similar problem.
The problem was described as the slab break detection sensor causing an emergency stop on a gang saw - sort of like an oversize bread slicer for granite blocks - the 'slices' come out 2 inches thick by about 6 feet x 8 feet. I had never seen a gang saw before, let alone fixed one. After the operator showed me the problem, I reviewed the schematic, and the slab break sensor was not tied into the emergency stop circuit. The error code traced back to an inverter alarm - over-voltage. By roundabout descriptions, when the slab break is detected, the drive motor (and 8 foot diameter flywheel) is braked to a stop. That was when the symptoms finally pointed to the braking resistors for the inverter. There were 3 braking resistors, and one had a burnt-out section. I spliced the resistor back together - less one turn to remove the burnt section. And then the slab break sensor problem was fixed.
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